Supersensitized silver halide photographic emulsion



1949- B. H. CARROLL ET AL 2,478,369

SUPERSENSITIZED SILVER HALIDE PHOTOGRAPHIC EMULSION Filed Dec. 29, 1945 FIG. 1.

'3, 3'- diefhy1-9- meihylselenaz'arbozyanlhe bromide FIG.2.

C 3,3; d1HIM-9-melh /seIe/7acarbac wz/he bromide I D 33'- dl'efhyl-fl -meThybe/enacarbagan/he bromide all/:15 'd/bmmopyr/Hine FIG.3.

' JOHN SPENCE IN VEN TORS MMQJ- km ATTO EYS Patented Aug. 9, 1949 SUPERSENSITIZED SILVER HALIDE PHOTOGRAPHIC EMULSION Burt H. Carroll and John Spence, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application December 29, 1945, Serial No. 638,492

15 Claims. (Cl. 95-7 This invention relates to sensitized photographic emulsions and to a process for preparing the same. This application is a continuation-inpart of our copending application Serial No. 466,796, filed November 24, 1942, now Patent No. 2,398,778 of April 23, 1946.

It is known that the distribution of spectral sensitivity of certain spectrally sensitized emulsions can be altered and an increase of sensitivity obtained in some spectral region, by incorporating certain additional sensitizing dyes in the spectrally sensitized emulsions. (See United States Patent 2,158,882, dated May 16, 1939 and 2,159,565 dated May 23, 1939.) The eiiect thus produced has come to be known as supersensitization. Supersensitization' of certain spectrally sensitized emulsions can also be effected by incorporating certain substantially colorless heterocyclic bases, viz. those containing an amino group, in the spectrally sensitized emulsions. (See United States Patent 2,177,635, dated October 31, 1939.) Supersensitization differs from hypersensitization which involves treatment of finished films or plate, an operation which normally reduces the pAg and increases the pH of the emulsion, with consequent decreased stability.

We have now found a new method for supersensitizing spectrally sensitized emulsions, which not only does not reducethe stability of the emulsions, but is especially valuable as a means of giving panchromatic sensitized emulsions of high speed and good color balance.

It is, accordingly, an object of our invention to provide new supersensitized photographic emulsions. A further object is to provide a process for preparing such emulsions. Still other objects will become apparent hereinafter.

In accordance with the invention, a photographic silver halide emulsion other than a chloride emulsion, e. g. silver chlorobromide, silver bromide or silver bromiodide emulsions, spectrally sensitized with a cyanine dye is supersensitized by incorporating in the emulsion certain pyridine bases. Our invention is directed principally to emulsions of such grain size that the emulsions give a substantially neutral-toned image in Eastman Kodak Companys D-76 developer, and. should not be confused with prior proposals to obtain blue-black tones in fine-grain emulsions by means of heterocyclic nitrogen bases. Moreover, our invention involves incorporation of the pyridine bases in the emulsions before exposure of the emulsion and should not be confused with proposals to develop with'color-iorming developers 2 silver-salt images, in the presence of certain heterocyclic nitrogen bases which contain a reactive methyl group.

The pyridine bases employed in practicing our invention are of a specific type and can be defined as pyridine bases containing, attached to at least one of the carbon atoms of the pyridine nucleus, a substituent selected from the group consisting of alkyl groups, alkoxyl groups, hydroxyalkyl groups, aryl groups, aryloxyl groups, alkylmercapto groups, arylmercapto groups, acyloxyl groups and halogen atoms. Exemplary of these pyridine bases are:

a-Picoline (2-methylpyridine) B-Picoline (B-methylpyridine) 'y-Picoline (4-methylpyridine) 2,3-lutidine (2,3-dimethylpyridine) 2,4-lutidine (2,4-dimethylpyridine) 2,6-lutidine (2,6-dimethylpyridine) 3,5-dibromopyridine z-ethylpyridine 2,3,4-trimethylpyridine 2-propylpyridine 2-benzylpyridine 2-phenylpyridine 3-phenylpyridine 3,5-dichlorpyridine 2-chloropyridine 3-ethoxypyridine 3-methylmercaptopyridine 3-acetoxypyridine etc.

The majority of cyanine dyes which are supersensitized by these pyridine bases are characterized by the fact that the dyes produce two types of sensitization depending upon conditions. Such diiierent types of sensitization are described by Leermakers, Carroll and Staud, J. Chem. Physics 5, 878 (1937) and by G. Schwarz, Sci. et Ind. Phot. 10, 233 (1939). When a cyanine dye of this type is used as a sensitizer in low concentration, it exhibits a sensitizing maximum displaced about 20 to mu toward the red from the absorption maximum in ethyl alcohol solution. On increasing the concentration of the dye, or upon digesting the emulsion containing the dye in the lower concentration, or both, a second maximum of sensitization develops at longer wavelengths, which may be accompanied by an increase in total optical sensitization. In some cases, a decrease in sensitivity at the first maximum can be detected." These phenomena are consistent with the hypothesis of two states of the sensitizing dye in an equilibrium which is controlled by concentration. The pyridine bases favor the formation of a second maximum which occasionally is appreciably displaced from the normal second maximum. The increase in sensitivity apparently corresponds to increased conversion of the dye to the state corresponding to the second maximum of sensitization. In some cases, the effect appears to correspond to a more complete conversion than has ever been obtained without a supersensitizer, and in any case the long wavelength sensitivity is better than can be obtained from the same concentration of dye without the pyridine base.

The following are exemplary of the cyanine dyes which are supersensitized in accordance with our invention:

3,1 -diethyl-6 -methoxy-2' -cyanine iodide 3,3-diethyl-9-methylthiacarbocyanine bromide 9-ethyl-3,3'-dimethylthiacarbocyanine bromide 5-chloro-3,3,9-triethylthiacarbocyanine iodide 5,5 dichloro 3,3',9 triethylthiacarbocyanine iodide 3,3-diethyl-9-methyl 4,5,4'5 dibenzothiacarbocyanine bromide 3,3 diethyl 9 methylselenathiacarbocyanine bromide 5' -d ethy1 9 methylselen thiac rbocyanine iodide 3,3d thyl-9-methylse1enacarbo yanine bromid The sensitizing dyes can be employed in any desired concentration. Ordinarily from 10 to mg. of dye per liter of emulsion will sumce to produce the optimum sensitizing effect. The methods of incorporating sensitizing .dyes in emulsions are well known to those skilled in the art. Ordinarily it is preferable to dissolve the dye in a water-miscible solvent, such as methanol or ethanol, before incorporating in the emulsion. One or more sensitizing dyes can be employed.

The amount of pyridine base employed is not critical. Usually the full supersensitizing effect is developed at a concentration of 0.10 t0 1.5 grams per liter of emulsion. At these concerntrations practically none of the pyridine bases has an appreciable effect on the pH of the emulsion. The pyridine bases can be added to the emuls ons with, before or after the sensitizing dye or dyes. More than one pyridine base can be employed. The pyridine bases are preferably, but not necessarily, diluted with a water-miscible solvent, such as methanol, before incorporation in the emulsions. The sensitizing dye or dyes and the pyridine base or bases can be added to the emulsions at any convenient stage of their preparation, but preferably to the washed, finished emulsions before coating.

The following examples will serve to illustrate the results obtained in accordance with our invention.

Example 1 A fast negative gelatino-silver-bromiodide developing-out emulsion was sensitized with 3,3'-diethyl-9-methylselenacarboeyanine bromide (20 mg. per liter of emulsion) and to separate portions of the spectrally sensitized emulsion were added various picolines, one to each portion. A lportion of the spectrally sensitized emulsion without any picoline, and. the other portions containing the picolines, were exposed through red (Wratten No. 25) and minus blue (Wratten No.

A fast negative gelatino-silver-bromiodide developing-out emulsion was sensitized with 3,3'-diethyl-9-methy1selenacarbocyanine bromide (20 mg. per liter of emulsion) and to a portion of the spectrally sensitized emulsion was added 3,5-dibromopyridine. A portion of the spectrally sensitized emulsion without the 3,5-dibromopyridine, and the portion containing it were exposed through red (W-ratten No. 25) and minus blue (Wratten No. 12) filters. The results are tabulated below:

Red Minus Blue 3, 5-dibromopyridine (00. per liter of emulsion) Speed Gamma Speed Gamma none 1.36 830 1.37 1.25 265 1.38 870 1.37

Example 3 A fast negative gelatinossilver bromiodide developing-out emulsion was sensitized with 3,3'-diethyl-9-methylselenacarbocyanine bromide (20 mg. per liter of emulsion) and to separate portions of the spectrally sensitized emulsion were added various lutidines, one to each portion. A portion of the spectrally sensitized emulsion without any lutidine, and the other portions containing the lutidines, were exposed through red (Wratten No. .25) and minus blue (Wratten No. 12) filters. The results are tabulated below:

I Bed. Minus Blue 7 lutidine (g. per liter of emulsion) Speed Gamma Speed Gamma none" 7 177 0. 80 .1, 020 0.82 2, 3-1ut d1ne, 1.25 500 0. 79 1, 250 0. 8O 2, elutidine, 1.25" 560 0. 81 1, 400 0. 81 2, fi-lutidine, 1.25.. .475 0. 67 1, 0. 76

The accompanying drawing illustrates graphically the supersensitizing effect obtained with three of our new [combinations in a gelatinosilver-bromiodide emulsion. Each figure in the drawing is a diagrammatic reproduction of two spectrograms. In Fi 1, curve A represents the sensitivity of a gelatino-silver-bromiodide emulsion containing 3,3-diethyl-Q-methylselenacarbocyanine bromide in a concentration of 20 mg. per liter of emulsion. Curve B represents the sensitivity of the same emulsion containing 3,3 diethyl 9 methylselenacarbocyanine bromide in a concentration of 20 mg. per liter of emulsion and containing, in addition, a-picoline in a concentration of 1.25 cc. per liter of emulsion. In Fig. 2, curve C represents the sensitivity of a gelatino-silver-bromiodide emulsion containing 3,3 diethyl 9 methylselenacarbocyanine bromide in a concentration of 20 mg. per liter of emulsion. Curve D represents the sensitivity of the same emulsion; containi g .3'-d y1- 9-methylselenacarbocyanine bromide in a concentration of 20 mg. per liter of emulsion and containing, in addition, 3,5-dibromopyridine in a concentration of 1.25 cc. per liter of emulsion. In Fig. 3, curve E represents the sensitivity of a gelatino-silver-brorniodide emulsion containing 3,3 diethyl 9 methylselenacarbocyanine bromide in a concentration of 20 mg. per liter of emulsion. Curve F represents the sensitivity of the same emulsion containing 3,3 diethyle 9-rnethylselenacarbocyanine bromide in a concentration of 20 mg. per liter of emulsion and containing, in addition, ZA-lutidine in a concentration of 1.25 g. per liter Cif emulsion.

Some of the pyridine bases, while effecting an increase of sensitivity (speed) in some spectral region, cause a decrease in others, and must be employed with this fact in mind.

Our invention is primarily directed to the customarily employed gclatino-silver-halide developing-out emulsions, such as gelatino-silverchlorobromide, gelatino-silver-br0mide and gelatino-silver-bromiodide developing-out emulsions, especially emulsions for development to blackand-white images by means of non-color-forming developers, e. g. hydroquinone-N-methyl-p-amino-phenol developers.

Emulsions prepared in accordance with our invention can be coated in the usual manner upon any desired support, such as cellulose nitrate support, cellulose acetate support, polyvinyl acetal resin support, metal support, glass support or paper support.

What we claim as our invention and desire to be secured by Letters Patent of the United States is:

1. A photographic silver halide emulsion selected from the group consisting of silver chlorobromide, silver bromide and silver bromiodide emulsions spectrally sensitized with a sensitizing cyanine dye and containing, as a supersensitizer, a pyridine base containing on a carbon atom of the pyridine nucleus, a member selected from the group consisting of alkyl groups, alkoxyl groups, halogen atoms, acyloxyl groups, alkylmercapto groups and aryl groups of the benzene series.

2. A photographic silver halide developing-out emulsion selected from a group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions spectrally sensitized with a sensitizing cyanine dye and containing, as a supersensitizer, a pyridine base containing on a carbon atom of the pyridine nucleus, a member selected from the group consisting of allryl groups, alkoxyl groups, halogen atoms, acyloxyl groups, alkylmercapto groups and aryl groups of the benzene series.

3. A photographic gelatino-silver-halide developing-out emulsion selected from the group consisting of gelatino-silver-chlorobromide, gelatino-silver-bromide and gelatino-silver-bromiodide developing-out emulsions spectrally sensitized with a sensitizing cyanine dye and containing, as a supersensitizer, a pyridine base containing on a carbon atom of the pyridine nucleus, a member selected from the group consisting of alkyl groups, alkoxyl groups, halogen atoms, acyloxyl groups, alkylmercapto groups and aryl groups of the benzene series.

4. A photographic gelatino-silver-bromiodide developing-out emulsion spectrally sensitized with a sensitizing cyanine dye and containing, as a supersensitizer, a pyridine base containing on a carbon atom of the pyridine nucleus, a member selected from the group consisting of alkyl groups, alkoxyl groups, halogen atoms, acyloxyl:

5. A photographic gelatino-silver halide dc-- veloping-out emulsion selected from the group consisting of gelatino-silver-chlorobromide, gelatino-silver-bromide and gelatino-silver-bromiodide developing-out emulsions spectrally sensitize-d with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wave length longer than that of the first maximum, said emulsion containing, as a supersensitizer, a pyridine base containing on a carbon atom of the pyridine nucleus, a member selected from the group consisting of alkyl groups, alkoxyl groups, halogen atoms, acyloxyl groups, alkylmercapto groups and aryl groups of the benzene series.

6. A photographic gelatino silver-bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higherconcentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, a picoline having the formula CSH'IN.

7. A photographic gelatino-silver-bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, a-picoline.

8. A photographic gelatino-silver-bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, a lutidine having the formula C'IHSN.

9. A photographic gelatino-silver-bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, 2,4-lutidine.

10. A photographic gelatino-silver-bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, 2,3-lutidine.

11. A photographic silver bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral'sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, a picoline having the formula C6H'1N.

12. A photographic silver bromiodide developing-out emulsion 'spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, a-picoline.

13. A photographic silver bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, a lutidine having the formula C'IH9N.

- 14. A photographic silver bromiodide developing-out emulsion spectrally sensitized with a 8 cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, 2,4-1utidine.

15. A photographic silver bromiodide developing-out emulsion spectrally sensitized with a cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of spectral sensitivity at a wavelength longer than that of the first maximum, said emulsion containing, as a supersensitizer, 2,3-lutidine.

BURT H. CARROLL.

JOHN SPENCE.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,158,883 Mees May 16, 1939 2,186,736 Schneider et a1 Jan. 9, 1940 OTHER REFERENCES Journal of Chemical Physics, 1937, vol. 5, pages 878-888. 

